This invention relates generally to jet engine systems and, more particularly, to fuel systems of jet engine aircraft having fuel jettison provisions.
It is common in aircraft systems design to include provisions for the jettison of fuel. The feature is provided to selectively reduce the overall weight of the aircraft to a level within the capability of the landing gear. This is necessitated when an aircraft having a full load of fuel is forced to land. Another time when a fuel jettison system is used is that prior to an emergency landing wherein it is preferable to reduce the amount of fuel on board to minimize the risk of significant fires. Further, it is of great importance to aircraft which operate out of airfields with short runways and which rely on aerial refueling to fill the tank after take-off of a partially fueled aircraft.
The normal approach for the jettison of fuel has been to provide auxiliary jettison pumps and associated piping to pump fuel from the aircraft fuel tanks to a safe overboard location, usually in the tail of the aircraft or at the ends of the wings. Such a system involves, in addition to the valves and piping, heavy auxiliary pumps which are not used for any other purpose and which comprise a significant load factor and installation expense. Also, the provision of fuel tight joints in aircraft compartments that would not otherwise contain fuel piping adds weight and hazards to safety. Further, to determine how much fuel has been jettisoned, a fuel jettison system generally relies on the existing system fuel tank quantity meters which commonly provide an inaccurate indication. Otherwise, if the jettison fuel flow quantity is desired, extra metering apparatus must be installed in the system.
It is therefore an object of this invention to provide a fuel jettison system which does not significantly add weight to aircraft.
Another object of this invention is the provision in a fuel jettison system for eliminating the use of auxiliary jettison pump, piping, metering apparatus, and associated hazards to safety.
Still another object of this invention is the provision for a fuel jettison system which does not impinge fuel on the airframe during periods of fuel jettison.
Yet another object of this invention is the provision for a fuel jettison system which is designed to be inoperable during periods in which the aircraft is on the ground and, for engines with an augmenter, during periods in which the afterburner is in operation.
Still another object of this invention is the provision for a fuel jettison system which is economical to fabricate and functional in use.
These objects and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.